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Investigators were also trying to track down surveillance video at a nearby bank where a man told cops he witnessed what he believed to be Hoffman, 46, buying drugs from two men several hours later on Saturday night.

The man told cops Hoffman looked "very sweaty" and "like s**t."

The actor was found dead from an apparent drug overdose by his screenwriter friend around 11am Sunday morning, police said. He was found with a needle stuck in his arm, sources told FOX411.

Police are looking into whether Hoffman had injected a lethal batch of heroin behind scores of recent deaths across the East Coast.

Meanwhile, a private wake for the actor is being planned for Thursday, while a public funeral will take place Friday in the same Manhattan church where Jacqueline Kennedy Onassis had hers.

Celebrity friends including Annie Leibovitz, Bobby Carnavale and Cate Blanchette were seen coming and going from his partner Mimi O'Donnell's house on Monday and Tuesday. She and Hoffman had separated, and she lived with their three children a few blocks from the rental apartment where he was found.